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#include <iostream>
#include <vector>

using namespace std;
using ll = long long;

int main()
{
    cin.tie(0)->sync_with_stdio();
    int n, k;
    cin>>n>>k;
    vector<int> vec(n);
    ll sum = 0;
    for(auto& x : vec) {
        cin>>x;
        sum += x;
    }
    for(int i=0; i<n; i++) {
        for(int j=i-1; j>=0; j--) {
            if(vec[j] < vec[j+1] - k) {
                vec[j] = vec[j+1] - k;
            } else {
                break;
            }
        }
        for(int j=i+1; j<n; j++) {
            if(vec[j] < vec[j-1] - k) {
                vec[j] = vec[j-1] - k;
            } else {
                break;
            }
        }
    }
    sum = -sum;
    for(auto x : vec) {
        sum += x;
    }
    cout<<sum<<"\n";
}